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Forum Index : Electronics : Simple Solar Regulator

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OA47

Guru

Joined: 11/04/2012
Location: Australia
Posts: 926

Posted: 01:08am 10 Apr 2016

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I recently required a simple solar regulator for a low power project and thought a zener circuit may do the job. Here is the circuit I used:

To my surprise the LED is always lit, even in total darkness. Can anyone explain why?

GM

oztules

Guru

Joined: 26/07/2007
Location: Australia
Posts: 1686

Posted: 02:57am 10 Apr 2016

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Interesting

...........oztulesEdited by oztules 2016-04-11

Village idiot...or... just another hack out of his depth

sparksandsmoke

Newbie

Joined: 14/05/2015
Location: Ireland
Posts: 12

Posted: 10:26am 10 Apr 2016

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As oztules says, interesting!

I see two possibilities. The first (least likely) is that the protection diode between the 300 Ohm res and the SLAB is leaking. The second (and the only plausible) source of voltage is the PV panel. Even in complete darkness the panel will be acting as an antenna for local fields, and it's a string of PN junctions (diodes) after all.

You haven't told us which type of LED, but a standard 5mm red LED will turn on at about 1.8V and many will illuminate at 2 or 3 mA (not at full brightness, of course), easily achievable from a PV panel in a moderately noisy area. Short out the PV panel when it's in darkness - if the LED goes out I claim my prize.

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